x1,y1,x2,y2,x3,y3 = eval(input("请输入3个顶点坐标："))
side1 = ((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2)) ** 0.5
side2 = ((x1 - x3) * (x1 - x3) + (y1 - y3) * (y1 - y3)) ** 0.5
side3 = ((x3 - x2) * (x3 - x2) + (y3 - y2) * (y3 - y2)) ** 0.5

s = (side1+side2+side3)/2
area = (s*(s-side1)*(s-side2)*(s-side3)) ** 0.5

print("面积为：",area)